Failed to Update MySQL table using Express JS - mysql

Question

I am facing difficulties to update the following tables (MySQL) by using Express Js.
productdb.discount
discount_id | discount_name | discount_percent
productdb.product
product_id | discount_id | product_price(original price) | product_latest_price(price after discount) |
It works on this way :
User update the existing discount table by inserting new discount name, percent and select relevant product that applies the respective discount from the checkbox. The input form is as below:
Hence when submit, it will return the discount info, including the discount_id, and the selected product in array-form according to the assigned product_id.
My concept of updating the database table is :
First, Update the discount table.
Then, Update all discount_id in product table to null according to the discount_id.
Update the product latest price to product price.
Update the discount_id to the product table according to the submitted product array.
Finally, Update the product_latest_price by calculating the result after multiple with discount_percent.
I wrote the Query in Express Promise based and it doesn't execute correctly as it failed to update the product_latest_price(Possibly due to async method). In fact, the code looks messy. Anyone have any idea on updating these tables in a more efficient way, or much cleaner code?
By the way, my code to execute the query is as below.
exports.discount_update = (discount_info, discount_id, product_id) => {
return new Promise((resolve, reject) => {
connectionPool.getConnection((connectionError, connection) => {
if (connectionError) {
reject(connectionError);
} else {
connection.query(`UPDATE productdb.discount SET ?
WHERE discount_id = ?`, [discount_info, discount_id], (error, result) => {
if (error) {
reject(error);
} else {
connection.query(`UPDATE productdb.product
SET discount_id = null, product_latest_price = product_price
WHERE discount_id = ?`, [discount_id], (error, result) => {
if (error) {
reject(error);
} else if (result.affectedRows >= 1) {
for (i = 0; i < product_id.length; i++) {
connection.query(`UPDATE productdb.product
SET discount_id = ?
WHERE product_id = ?`, [discount_id, product_id[i]], (error, results) => {
if (error) {
reject(error);
} else {
connection.query(`UPDATE productdb.product AS product
JOIN productdb.discount AS discount
ON product.discount_id = discount.discount_id
SET product.product_latest_price = product.product_price - product.product_price * (discount.discount_percent) / 100
WHERE product_id = ?`, [product_id[i]], (error, result) => {
if (error) {
reject(error);
} else if (result.affectedRows >= 1) {
resolve(result)
} else {
resolve(result)
}
})
}
})
}
}
})
}
})
}
})
})
}